Semiconductor LEDs have replaced conventional incandescent, fluorescent and halogen light sources in many applications due to their small size, reliability, relatively inexpensive cost, long life and compatibility with other solid state devices. In a conventional LED, an N-type gallium arsenide substrate that is properly doped and joined with a P-type anode will emit light in visible and infrared wavelengths under a forward bias. In general, the brightness of the light given off by an LED is contingent upon the number of photons that are released by the recombination of carriers inside the LED. The higher the forward bias voltage, the larger the current and the larger the number of carriers that recombine. Therefore, the brightness of an LED can be increased by increasing the forward voltage. However due to many limitations, including the ability to dissipate heat, conventional LEDs are only capable of producing about six to seven lumens.
Recently a new type of LED has been developed for use as a flash in camera phones. The Luxeon®. Flash LXCL-PWF1 and LXCL-PWF2 LEDs commercially available from Lumileds Lighting of San Jose, Calif., USA are capable of producing forty lumens at one ampere, and eighty lumens at one ampere, respectively. These surface mounted LEDs are only one millimeter in height and they have a very small footprint (2.0 .times. 1.6 mm or 3.2 .times. 1.6 mm, respectively). They are rated for 100,000 flashes at one ampere, and one hundred and sixty-eight hours of DC (flashlight/torch mode) at 350 milliamperes.
While these new flash LEDs offer increased brightness over conventional LEDs they still suffer from problems associated with heat dissipation and inefficient distribution of light.